Degradation of unsaturated fatty acids



United States Patent O DEGRADATION F UNSATURATED FATTY ACIDS Werner Stein, Dusseldorf-Holthausen, and Horst Hennig,

Dusseldorf-Oberkassel', Germany, assignors to Henkel & Cie. G.m.b.H., Dusseldorf-Holthausen, Germany, a German corporation No Drawing. Application February 5, 1957 Serial No. 638,216

9 Claims. (Cl. 260-413) This invention relates to new and useful improvements in the degradation of unsaturated fatty acids.

- Alkali soaps of unsaturated fatty acids, which are free from alcoholic hydroxyl groups may be degradated to soaps of the corresponding saturated fatty acids containing 2 less carbon atoms than the initial unsaturated fatty acids by heating at a temperature above about 280 C. and preferably at a temperature of about 320 C. in the presence of an alkali hydroxide in accordance with the well-known method of Varre'ntrap'p. The degradation occurs with the evolution of hydrogen and the reaction Qrnay be catalyzed with cadmium or cadmium'compounds. One object of this invention ifs'an improved method for the above-described degradation. This, and still Qfurther'objects will become apparent from the following .desciiption: V I Y In accordance with the invention, it has now been found that the degradation of unsaturated fatty acids which are free from alcoholichydroxyl groups by heating in the'presence of an alkali is catalyzed by' lead, lbism'uth, or thallium. In accordance with the invention the heating in the presence of the excess alkali is therefore effected in the additional presence 'of at least one of leatlfbi'smuth, and thallium. The catalyst metal, i.e.,

the lead, bismuth, or thallium may be added in the form of a'mixture, alloy, or a compound of the metal.

The process in accordance with the invention is suitable for the degradation of any of the known, unsaturated, fatty acids which could conventionally be degraded by heating in the presence of an excess of alkali. The unsaturated fatty acids are subjected to the degradation in the form of their alkali soaps, and the starting materials inthe process in accordance with the invention include any of the alkali soaps of unsaturated fatty acids which are free from alcoholic hydroxyl groups and which may be derived from fats of vegetable or animal origin or from any desired mixture containing unsaturated fatty acids. There may also be used fatty acid fractions from which the saturated portions have been removed to a greater or lesser extent by conventional methods.

The degradation reaction is believed to occur with a migration of the double bond toward the carboxyl group and a splitting off of acetic acid. An excess of alkali which theoretically amounts to one times the average number of double bonds per molecule in mols of alkali 'quantity theoretically required. This applies in particular tolgthe partial degradation of fatty acid mixtures having large portion of unsaturated fatty acids with more than lone double bond in the molecule. As the unsaturated R 2,921,084 7 Patented Jan. 12, 1960 fatty acids having multiple double bonds are more easily degraded than those having a single double bond, it is possible to selectively degrade the unsaturated fatty acids with multiple double'bonds to a shorter chain length with a decrease in the unsaturation down, if desired, to monounsaturates, while the initially present mono-unsaturated fatty acids remain substantially unchanged. If, however, the unsaturated fatty acids present are to be convertedv as completely as possible into saturated fatty acids, there is preferably employed a quantity of alkali hydroxide, which is at least and preferably to 200% of the quantity theoretically required. It is, of course, possible touse much higher quantities of alkali, as, for example, up to 400% of the amount theoretically required,

but operation with such large excesses of alkali hydroxide is uneconomic, since the unnecessarily high excess of alkali used remains in the soap formed, and is destroyed upon the working up of the soap to fatty acids.

The alkalis used are preferably alkali hydroxides, and inparticular sodium or potassium hydroxide or their mixtures.

The degradation reaction may be effected either in the presence or absence of water. When working without pressure, any water present in the reaction mixture evaporates practically completely, so that if the presence of water is desired, the use of pressure becomes necessary. The pressure in the reaction vessel generally establishes itself in accordance with the reaction conditions,

.andcan, in general reach values of up to about 200 reaction vessel during the reaction, care should be taken that the pressure does not drop below the vapor pressure of the water present in the reaction mixture if the reaction is to be effected in the presence of water. Operating in the presence of water has the advantage that the formation of non-saponifiable products during the reaction is extensively suppressed. For this purpose there is generally required a water content of at least 20% by weight referred to the fatty acid present in the reaction mixture, though amounts of water of about 50 to 100% by weight are preferably used. Although the reaction will still. occur with higher dilution, operation is generally not effected with a water content of more than about 400% by weight. .The pressures occurring during the reaction are dependent on the extent to which the reaction vessel is filled, or whether or not hydrogen is blown off during the reaction and up'on the reaction of temperature used, which may rise, for example, to about 420 C. In general, it is not necessary to use temperatures above about 400 C., and, if operation is effected without pressure, and thus in. the absence of water, it is generally not advisable to employ a reaction temperature above about 350 C. v p The reaction is generally effected by merely heating the alkali soap of the fatty acid in the presence of the excess alkali hydroxide and the catalyst metal in accordance with the invention, as, for example, in a closed :pressure vessel, such as an autoclave, and preferably with stirring. The alkali soap may be formed in situ by initially contacting the unsaturated fatty acid with an amount of alkali hydroxide sufiicient to form the soap and leave the excess of alkali hydroxide required for the degradation. In general, the process may be effected using all the known embodiments of the Varrentrapp reaction, as, for example, those described in connection with French Patent No. 1,037,261.

The catalytic action of the catalyst in accordance with 3 the invention may already be noted upon the addition of 0.05% by weight metal, referred to the fatty acid present in the reaction mixture. It is preferable, however, to operate with larger quantities of catalyst, as, for example, -0.5'to 20% by weight metal, though larger quantities 'may be used, so that, for example, the metal used is present :in equivalent amounts to the fatty acid present. It is also .possible to use the entire fatty acid in the form of its salts with the catalyst metal, particularly when it is desired to separate the unsaturated fatty acid in the form of is metal salts from theaccompanying saturated fatty acids formed.

The catalysts used in accordance with the invention may be employed in the form of free metals or their compounds, and particularly in the form of compounds which are reduced under the reaction conditions to the free metals. Such compounds which, may be added to the reaction mixture, include, for example, the carbonates,

bicarbonates, oxides, or hydroxides of lead, bismuth, or

thallium. It is, of course, also possible to add the metal in the form of compounds which form hydroxides or oxides withthe alkali hydroxide under the reaction condi tions. These compounds include, for example, chlorides, bromides, iodides, sulfites, sulfates, phosphates, nitrites, nitrates, forrnates, acetates, oxalates, stearates, oleates, ricinoleates, benzoates, phthalates, benzene sulfonates, or .paraffin 'sulfonates, as well as salts of other inorganic or organic acids, and in particular, the mineral acids or the carboxylic of sulfonic acids.

If the catalyst metals are amphoteric, they may also be used in the form of salts in which the metal is in the acid radical, as, for example, plumbites or plumbates in the case of lead. Complex salts of the metals can also be .added. It is also possible to use metallorganic compounds, as, for example, tetraethyl lead, diphenyl lead or other metal alkyls or aryls as the catalytically active metal compounds.

The lead, bismuth and thallium or their compounds may also be used in combination with each other to particular advantage. The metals may also be used in the form-of mixtures or alloys with each other or with other .metals, and it is of particular advantage to use the metal in the form of a low-melting alloy, as, for example, an alloy having a melting point below the reaction temperature, as the same is of special advantage in connection with the recovery of the catalyst, since it allows separating the liquid metal from the reaction mixture, which is of great value, both in connection with continuous operation and batch operation.

It is, of course, possible, even when using the pure metal lead, thallium or bismuth, to operate above the melting points of the same (lead-327 C.; thallium- 303 C.; and bismuth-271 C.), which, as a matter of -fact has already been done in the case of cadmium (321 C.), but when operating in such a manner it is necessary to effect the separation of the liquid metal from the reaction mixture above its melting point, since otherwise the liquid metal may solidify at a different colder portion of the apparatus and result in clogging. When, however, operating with alloys which have melting points which are relatively far below the reaction temperature, it is possible to separate the catalyst even at lower temperatures in the liquid condition from the reaction mixture, the higher specific weightsof said alloys promoting the separation, so thatthe liquid metals may easily be separated by allowing the same to settle out at the bottom of the vessel in question. The separation of the metal may be effected at any desired place, as, for example, in the reaction vessel itself, or in a special separator after dilution ofthe reactionmixture with water. The alloysseparated from the reaction -=mixture may then either be recycled to the process as 'being preferably selected. slight additions of a foreign metal to a catalytically active metal are su'fiicient to considerably reduce the melting point of the latter, the use of eutectic mixtures is not absolutely necessary if it is desired to operate with'a thereof by weight. the quantities of catalystgiven-below refers to the quan- 't1ty of the active component, to be used in accordance point of the catalytically active metal per se. There are preferably used, however, low melting point alloys, as, for example, those having melting points below 300 C., and preferably below about 200 C. 7

Among the alloys of lead, thallium, and bismuth, there is a particularly large number having low melting points, and in many'cases melting points below C. In accordance with the present invention there are used, for example, alloys of the systems The metals to be used in accordance with the invention or their alloys can, however, also be combined with other metals which in themselves are inactive, for instance, with metals which melt at a lower temperature than the metals to be used in accordance with the invention, or with metals which melt at a higher temperature. This includes indium (156 C.), tin (232 C.) and antimony (630 C.). The following table contains metals or metal alloys having melting points below 300 C.

40.95 Bi+22.10 Pb+18.10 In+10.65 Sn As alloys, there may be used alloys of two or more components, the composition of low-melting eutectics Since, however, frequently low melting mixture. QAccording'ly, the alloys can contain at least 5% by weight of the active metal to be used in accordance'with the invention and preferably 10 to In case of the use of alloys,

with the invention, present in the alloy.

The invention, however, does not extend only to the use of 'lowmelting alloys, but also to the use of pure m'etals or alloys which me'lt'at ahigher'temperature than the Pure metals. When using such alloys it is possible to operate below the melting point of the metal and thus avoid the melting-of the metal in the reaction mixture.

The metal then remains'suspended in finely divided form -in the reaction mixture, and, after the dissolving of the reaction mixture in water, can be separated/and added to new reaction batches.

The followingexamples are given by'way of'illustration and not limitation:

a For the 'carrying out of the experiments describedin the examples, there was used technical powdered sodium amples. The batches were fille'd into tubes of nickel (Example 1), of V4a-steel (Examples 2-5) or copper (Examples 6 and 7), and "placed, in these tubes, in an autoclave provided with an agitator, In the autoclave thebatches were heated to the temperatures indicated. The autoclave remained closed during the entire reaction, so that neither water,which had formed upon the neutralization of the-fatty acidwith alkali hydroxide, nor which had been added to thereaction batch, nor hydrogen, could escape from the reaction batch. After cooling to room temperature, the autoclave was opened, the tubes containing the reaction product were removed, and the reaction, product was dissolved in hot water. The catalyst metal collected to a large extent on the bottom of .the" tubesso' that the solution of the reaction product in water could'be directly poured all from the metal. From the aqueous solution the fatty'acid was separated by hydrochloric acid and then washed neutral with water. i 1 p The tubes, the agitators of the autoclaves, and the thermometer connections were freed of small amounts of catalyst metal adhering thereto before each new test by treatment with dilute nitric acid.

Since the yields in connection with the process are practically quantitative, the yields were not determined in the individual experiments. However, the characteristic values of the degraded fatty acids were given.

Example 1 Batch:

500 grams soya fatty acid, refined (acid number =205, saponification number=209, iodine number=93,-solidification point=28.7 C., unsaponifiables=1.2%

158 grams NaOH 20 grams PbCl,

Reaction:

4 hours at 300' C., maximum pressure 86 kg./cm. Fatty acid:

Acid number=200, saponification number=l98,

iodine number=36, solidification point=32.7 C.

Example 2 Batch:

300 grams fatty acid according to Example 1 102 grams NaOH 21 grams Bi(NO -,'5H O Reaction:

4 hours at 300 C., maximum pressure 82 kg./cm.' Fatty acid:

Acid number=l94, saponification number=20l,

iodine number=37, solidification point=32.7 C.

Example 3 Batch:

500 grams fatty acid in accordance with Example 1 170 grams NaOH 19.5 grams TlNO Reaction:

4 hours at 300 0., maximum pressure 91 kgJcm. Fatty acid:

Acid number=l93, saponification number=l95,

iodine number=34, solidification point=33.1 C.

Example 4 Batch:

' 300 grams fatty acid in accordance with Example 1 100 grams NaOH 16 grams KOH 20.2 grams PbCl, Reaction:

2 hours at 300 C., maximum pressure: 62 kg./cm. Fatty acid:

Acid number=206, saponification number=206, iodine number=3l, solidification point=33.5 C., unsaponifiables=5.$%

I Batch:

When carrying out theisame experiment without addition ofcatalyst, there 'was obtained a fatty acid having the following characteristic values: Acid number=197, saponification number=200, iodine number=4l, solidification point=33", C., unsaponifiables =8.2%. Example 5 v29.2 grams PbCl, Melting point of the catalyst 6.0 grams SbCl alloy: 250 C. Reaction:

5 minutes at 300 0., maximum pressure: 64 kg/em. 1 1 Fatty acid:'

Acid number=2l1, saponification number=2l9, iodine number=43, solidification point=27s8 C., unsaponifiables=3.0%

When the same batch, without catalyst, was heated for 4 hours at 300 C., there was obtained a fatty acid having the following characteristic values:

Acid number=198, saponification number=20l, iodine number=34, solidification point=28.2 C., unsaponifiables=9.4%.

. Example 6 Batch:

200 grams fatty acid according to Example 1 69 grams NaOH 214 grams water 12 grams Bi(NO -5H O 5.3 grams PbCl 0.94 grams CdO Reaction:

2 hours at 350 C., maximum pressure: 180 kg./cm. Fatty acid:

Acid number=226, saponification number=226, iodine number=22.6, solidification point=32.1' C., unsaponifiables=2.1%

Melting point of the catalyst alloy: 92 C.

Example 7 Batch:

250 grams technical oleic acid (acid number=l 97, saponification number=202, iodine number=82, solidification point=6 C., unsaponifiables: 0.8%)

grams NaOH 8 grams water 5529 Melting point of the grams 3 o 1.2 grams o catalyst alloy. 127 C. Reaction:

2 hours at 350 0, maximum presure: 98 kg./cm.= Fatty acid:

Acid number=209, saponification number=209, io-

dine number =33, solidification point=33.6 C., unsaponifiables=4.7%.

a temperature of aboutr300 C.,

thallium, mixtures thereof, alloysv thereof and compounds ofisaid metals and in which said heating iseffected at 2. Improvement according to claim 1 in which said metal compound is a member selected from thegroup consisting of metal chlorides and metal nitrates.

3. Improvement according to claim 1, in which said group member is present in amount of about .05 to 20% by weight, based on said fatty acid.

4. Improvement according to claim 1, in which said group member is in the form of an alloy having, a melting point below the temperature to which said heating is effected. I

5.-1mprovement according to claim 4, which'includes separating said group member from thereaction mixture in the liquid state. .7

-6.:Improvement' according to claim '5, which includes recycling the separated group member.

7. Improvement according to claim 6, whichinclude's converting said'separated group member to ametal compo n p i o aid ccyc ine. t .8. Imp ov e c o dinst acla nz in which sa group'member is initially added in the form of a metal compound. I W v 9,. Improvement according to claim 1, in which said alkali hydroxide is a member selected from the group consisting of, sodium hydroxide, and potassium hydroxide. e

References Cited raise file at inseam FOREIGNPATENTS I ,Greasmnain Aug. 11,1954 Great Britain Aug. 11, 1954 1 I omen ger'anauces Catalysis in Organic Chemistry, Sebatier, D. Van Nostrand Co., N.Y., 1922,-page .315. 

1. IN THE METHOD FOR DEGRADATING UNSATURATED FATTY ACIDS, IN WHICH AN ALKALI SALT OF AN UNSATURATED FATTY ACID, FREE FROM ALCOHOLIC HYDROXYL GROUPS IS HEATED IN THE PRESENCE OF AN ALKALI HYDROXIDE, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE HEATING IN THE PRESENCE OF AT LEAST 0.05% BY WEIGHT A CATALYST BASED ON SAID FATTY ACID SELECTED FROM THE GROUP CONSISTING OF LEAD, BISMUTH, THALLUIM, MIXTURES THEREOF, ALLOYS THEREOF AND COMPOUNDS OF SAID METALS AND IN WHICH SAID HEATING IS EFFECTED AT AT A TEMPERATURE OF ABOUT 300* C. 